Charity watchdogs are to crack down on fundraisers who send out unsolicited gifts to make potential donors feel guilty enough to give money.

The Institute of Fundraising has changed its code of practice to stop charities sending items such as umbrellas, slippers, aprons and Christmas cards when they are used to "generate a donation primarily because of financial guilt or to cause embarrassment".

Last year there were more than 2,600 complaints about direct mailing from charities. The Charity Commission will today release research showing 50% of people believe charities are using more dubious fundraising techniques; 20% of people gave more than £200 to charity in the past year.

Jon Scourse, the chief executive of the Fundraising Standards Board, which will police the new code, said a recent mailing from the Diabetes Research & Wellness Foundation (DRWF) was the kind that could be in breach of the sector's new self-regulation. The charity sent slippers to potential donors with a letter explaining the dangers to diabetics of cuts on their feet that can lead to amputations. It included a response for the recipient to post back, reading: "I love these slippers and I agree we must all treat our feet well to prevent the tragic and needless amputations caused by diabetes. Enclosed is my gift to further diabetes research."

Scourse said: "Elderly people in particular are vulnerable to feeling guilty. They end up keeping the gift and feel they should make a donation."

Sarah Bone, the DRWF's chief executive, said: "The slipper pack may well be emotive and the aim of the pack is to generate financial support, but they are not meant to make people feel guilty."

From today the public will be able to complain to the FRSB. The board may demand a campaign is stopped and a charity could be expelled from membership.